Recently, the generalization of telecommunication services, and the emergence of various multimedia and high-quality services have resulted in the increase of demands to communication services. To actively copy with these trends, the capacity of a communication system should be increased in a wireless communication environment rather than in a wired communication environment. This is because in the wireless environment, available frequency spectrum is extremely limited and should be shared, and the need for wireless communication services gets increasing fastly by its inherent unthetheredness.
The capacity of wireless communication systems can be increased by allocating a greater bandwidth and enhancing the efficiency of a given radio resource.
Various methods to increase the efficiency of the given radio resource have been developed, Among them, a space-time coding method has attracted considerable attention in the wireless communication environment since it can improve the reliability of data transmission in a wireless communication system by using additionally the spatial dimension for resource utilization without bandwidth expansion and/or increase transmission capacity through parallel transmission using spatial multiplexing.
In a like manner, transmission capacity of wireless communication systems may be remarkably increased by employing MIMO techniques.
A space-time block coding method proposed by Alamouti (entitled “A simple transmit diversity technique for wireless communications”, IEEE JSAC, vol. 16, no. 8, October 1998) is a representative transmit diversity technique that overcomes multipath fading over wireless channels by using multiple antennas both at the transmitter and receiver. The above space-time block coding method uses only two transmit antennas and can achieve the full diversity by providing the diversity order corresponding to a product of the number of transmit antennas and the number of receive antennas. However, the above methods can transmit only two data symbols during two time slots through two transmit antennas, thus resulting in a transmission rate of 1, and no spatial multiplexing gain is achieved irrespective of the number of receive antennas. Furthermore, this method cannot be applied to the case of more than three transmit antennas.
Bell Lab's V-BLAST (Vertical Bell Laboratories Layered Space-Time) system (entitled “Detection algorithm and initial laboratory results using V-BLAST space-time communication architecture”, IEEE, Vol. 35, No. 1, pp. 14-16, 1999) is a representative method for achieving a spatial multiplexing gain. In the V-BLAST system, each transmit antenna transmits a different signal with the same transmission power and data rate, and a receiver performs the three consecutive processes of detection ordering, interference nulling, and interference cancellation to remove undesired interference signals, thereby to increase a signal-to-noise ratio (SNR) when the receiver detects the transmitted signal. In the V-BLAST system, the full spatial multiplexing gain is maintained since independent data signals corresponding to the number of transmit antennas can be simultaneously transmitted if the number of transmit antennas is equal to or greater than the number of receive antennas. However, this method requires the number of receive antennas to be equal to or greater than the number of transmit antennas and achieves the full multiplexing gain with no diversity gain. Moreover, once a data symbol is restored with error, the erroneous data is propagated to the following signal detection processes thereby resulting in severe performance degradation.
Meanwhile, a tilted Quadrature Amplitude Modulation (QAM) code proposed by Yao and Wornell (entitled “Structured space-time block codes with optimal diversity-multiplexing tradeoff and minimum delay,” Globecom, pp. 1941-1945, 2003) is a space-time code for providing full diversity and full rate (FDFR) that achieves an optimal diversity-multiplexing tradeoff proposed by Zhang and Tse. The tilted QAM code is a short space-time block code with code length of two for a system with two transmit antennas and two receive antennas, and the rotation of QAM constellations is used to obtain the full diversity gain while preserving the full multiplexing gain. However, this algorithm cannot obtain a full coding gain because it uses simple rotation of a signal, and may be exploited only with a two transmit antenna and two receive antenna system. The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and therefore, unless explicitly described to the contrary, it should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.